Waveform detection of states and faults in plasma inverters

ABSTRACT

A system for determining an operational state of an atmospheric pressure plasma. The system has a transformer for coupling power into the atmospheric pressure plasma, a current sampling circuit configured to sample at least one current pulse flowing through a primary winding of the transformer, and a programmed microprocessor configured to determine, from a waveform of the current pulse, the operational state of the atmospheric pressure plasma. The operational state is one of: a no plasma state, a plasma origination state indicative of an ignited arc expanding into a plasma by gas flow thereinto, and a plasma maintenance state indicative of the plasma being expanded.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.17/085,475, filed Oct. 30, 2020 which claims priority to PCT/US/20/28401(entire contents of which are incorporated herein by reference), filedApr. 16, 2020 entitled “Waveform Detection of States and Faults inPlasma Inverters,” which is related to and claims priority to U.S. Ser.No. 62/834,947 filed Apr. 16, 2019, entitled “Waveform Detection ofStates and Faults in Plasma Inverters,” the entire contents of which areincorporated herein by reference. This application is related to andclaims priority to U.S. Ser. No. 62/834,545 filed Apr. 16, 2019,entitled “Frequency Chirp Resonant Optimal Ignition Method,” the entirecontents of which are incorporated herein by reference. This applicationis related to U.S. Ser. No. 62/834,119 filed Apr. 15, 2019, entitled“Asymmetrical Ballast Transformer,” the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION Field of Invention

The invention relates to ways to indirectly detect faults andoperational states of plasmas.

Discussion of the Background

Plasma technology applications include, for example, semiconductor,various surface modifications, and coatings of reflective films forwindow panels and compact disks. Plasmas ranging in pressure from highvacuum (<0.1 mTorr) to several Torr are common and have been used forfilm deposition, reactive ion etching, sputtering and various otherforms of surface modifications. For example, gas plasmas are known forthe treatment of plastics and molded substrates (e.g., thermoplasticolefin substrates used as bumpers and fascia in the automotive industry)to improve adhesion of subsequently applied coating layers. Themodification typically is a few molecular layers deep, thus bulkproperties of the polymeric substrate are unaffected. A primaryadvantage of using plasma for such purposes is that it results in an“all dry” process that generates little or no effluent, does not requirehazardous conditions such as toxic chemicals or high pressures, and isapplicable to a variety of vacuum-compatible materials, including, interalia, semiconductors, metals, glasses, polymers, composites and ceramics

It is commonly known to use plasma, typically O₂ plasmas, as a means ofremoving hydrocarbon and other organic surface contaminants from varioussubstrates. However, because of the short lifetime of these reactantsand their line-of-sight reactivity on the surface, these highlyactivated reactants are not especially well-suited for surface cleaningof irregular surfaces, unpolished or roughened metallic surfaces, orsurfaces having a three-dimensional topography.

Also, use of plasma at reduced pressures has several disadvantages inthat the substrate to be treated or cleaned must be placed under vacuumand must be capable of surviving under such reduced pressure conditions.Use of a plasma at or above atmospheric pressure avoids these drawbacks.

Yet, the coupling of power into atmospheric pressure plasmas is notstraight forward, especially during the time frame when the gastransitions into a plasma. The gas presents a high impedance to thepower source, while the resultant plasma appears as a low impedance loadto the power source, with the transition from these states resulting ina dynamic change in impedance and current surges.

SUMMARY

In one embodiment of the invention, there is provided a system fordetermining operational states of an atmospheric pressure plasma. Thesystem has a power coupler for coupling power into the atmosphericpressure plasma, a current sampling circuit configured to sample atleast one current pulse flowing through a primary winding of thetransformer, and a programmed microprocessor configured to determine,from a waveform of the current pulse, the operational state of theatmospheric pressure plasma. The operational state is one of: a noplasma state, a plasma origination state indicative of an ignited arcexpanding into a larger volume of plasma by gas flow thereinto, and aplasma maintenance state indicative of the plasma being expanded.

In one embodiment of the invention, there is provided a system fordetermining operational states of an atmospheric pressure plasma. Thesystem has a power coupler for coupling power into the atmosphericpressure plasma, a current sampling circuit configured to sample atleast one current pulse flowing to a plasma-generating region, and aprogrammed microprocessor configured to determine, from a waveform ofthe current pulse, the operational state of the atmospheric pressureplasma. The operational state is one of: a no plasma state, a plasmaorigination state indicative of an ignited arc expanding into a largervolume of plasma by gas flow thereinto, and a plasma maintenance stateindicative of the plasma being expanded.

In one embodiment of the invention, there is provided a method fordetermining an operational state of an atmospheric pressure plasma usingthe system described above.

In one embodiment of the invention, there is provided a ballasttransformer whose operation is controlled in part by the systemdescribed above.

It is to be understood that both the foregoing general description ofthe invention and the following detailed description are exemplary, butare not restrictive of the invention.

BRIEF DESCRIPTION OF THE FIGURES

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A is a schematic of an atmospheric plasma source;

FIG. 1B is a schematic of a system for coupling power to an atmosphericplasma;

FIG. 2 is a schematic circuit model of a ballast transformer coupled toa variable resistance load;

FIG. 3 is a schematic of an asymmetrical ballast transformer of thepresent invention;

FIG. 4 is a schematic graph of frequency vs impedance sweep of using aballast transformer for different loads;

FIG. 5 is a schematic graph of a current transfer frequency sweep fordifferent loads coupled to a ballast transformer, one with no load(pre-ignition of plasma) and the other at post ignition;

FIG. 6 is a schematic graph of a current transfer frequency sweep for apost ignition plasma load and a fully developed plasma load;

FIG. 7 is a schematic depiction showing a computer analysis of thecircuit shown in FIG. 1 driven with a square wave drive;

FIG. 8 is a schematic depicting a current waveshape for a plasmaorigination state;

FIG. 9 is a schematic depicting a simulated current waveshape for adeveloped plasma maintenance state;

FIG. 10 is a schematic depicting computed current transfer functionamplitudes for various output loads;

FIG. 11 is a current amplitude spectrum from a square wave drive into aballast transformer for nominal plasma impedance;

FIG. 12 is a current amplitude spectrum from a square wave drive into aballast transformer for a 1 Ohm short;

FIG. 13 is a schematic depicting a system on a chip (SOC) microprocessorfor production of output waveforms driving a ballast transformer;

FIG. 14 is a schematic depicting a current sense transformer (CST) formeasuring primary current in the ballast transformer of FIG. 13 ; and

FIG. 15 is a flow chart detailing a method of the present invention fordetecting an operational state of an atmospheric pressure plasma.

DETAILED DESCRIPTION OF THE INVENTION

In various embodiments, the present invention provides systems andmethods for determining operational states of an atmospheric pressureplasma. As used herein, atmospheric pressure refers to the absolutepressure of the ambient in which the device generating the “atmosphericpressure” is disposed. In various embodiments, the present inventionuses a programmed microprocessor to determine (from a waveform of acurrent pulse driving a ballast transformer coupled to the plasma) anoperational state of the atmospheric pressure plasma. The operationalstate is one of a no plasma state, a plasma origination state indicativeof a gas-flow expansion of an arc ignited in the plasma chamberexpanding into a plasma by gas flow thereinto, and a plasma maintenancestate indicative of sustaining the plasma in the plasma chamber.

Atmospheric Plasma Source

FIG. 1A is a lengthwise cross-sectional view of an exemplary AP plasmasource 102 to which the operational states can be determined. The APplasma source 102 includes an axially elongated plasma-generatingchamber 104 or other structure that serves as a ground electrode forgenerating a plasma and that serves as a conduit for flowing gases intothe plasma. The plasma-generating chamber 104 may be enclosed in anelectrically- and thermally-insulating housing (not shown). A “hot” orpowered electrode 106 is located in the plasma-generating chamber 104.Electrical connections to the hot electrode 106 may be made through adielectric structure 108 located at the proximal end of or in theplasma-generating chamber 104. One or more gas inlets 110 may be formedthrough the dielectric structure 108 in fluid communication with theplasma-generating chamber 104. The gas inlets 108 may be placed in fluidcommunication with a gas supply source. Accordingly, the gas inlets 110provide a flow path for plasma-generating gas fed to plasma-generatingregion 112 within the plasma-generating chamber 104 proximate to the hotelectrode 106. In operation, the plasma is generated in region 112 andsubsequently flows (with the gas flow) toward a nozzle 114 positioned ata distal end of the plasma-generating chamber 104.

Generally, operating parameters associated with the AP plasma source 102are selected so as to produce a stable plasma discharge. Control 116having a processor is used for setting and controlling the operatingparameters which depend on the particular application ranging, forexample, from nanoscale etching of micro-fabricated structures ordevices (e.g., MEMS devices) to removing large areas of paint fromaircraft carriers. Examples of operating parameters are provided belowwith the understanding that the teachings herein are not limited by suchexamples. In the case of generating an air plasma, the rate at which theair is fed to the AP plasma source 102 may range from 1×10⁻⁶ SCCM to1×10⁶ SCCM. The feed pressure into the AP plasma source 102 may rangefrom 1 Pa to 1×10⁷ Pa. The power level of the electrical field drivingthe plasma may range from 1×10⁻⁶ W to 1×10⁶ W. The drive frequency ofthe electrical field may range from DC (0 GHz) to 100 GHz. Theseparation distance, i.e. the distance from the nozzle exit to theexposed surface of the material to be removed, may range from 1×10⁻⁶ mto 40 cm. The scan speed, i.e. the speed at which the AP plasma source102 may be moved across (over) the surface of the material, may rangefrom 1×10⁻⁴ m/s to 10 m/s. Related to the scan speed and power is thetime averaged power density. Also related to the scan speed is the dwelltime, i.e., the period of time during which a particular area of thematerial is exposed to the plasma plume, which may range from 1×10⁻⁹ sto 1×10³ s.

In one embodiment of the present invention, AP plasma source 102 has aconverging nozzle (i.e., a straight conical cross-sectional flow areawithout being followed by a diverging section), has been fabricated andevaluated. The AP plasma source repeatably and reliably produces aplasma plume which may include the production of shock waves. The APplasma source generates an air plasma using air at about roomtemperature as the feed gas. The air may be fed to an AP plasma sourceof this type at a pressure ranging from 30-110 psi and at a flow rateranging from 1-7.5 CFM. In another example, the pressure range is 65-95psi. In another example, the flow rate range is 1-4 CFM. Pressureshigher than 110 psi may also be implemented to produce shock waves. In amore general example, the pressure may be 30 psi or greater and the flowrate may be 1 CFM or greater.

Under these conditions, at plasma ignition, there is a (typically small)arc from the driven or “electrically hot” electrode to the chamber wall,and the gas flow “expands” the spatially confined arc into a diffusedvolume of plasma or plasma plume 118 extending out of the outlet 114.The electrical impedance before and after plasma ignition and during theexpansion of the arc vary greatly as detailed below.

The present invention provides as shown in FIG. 1B a system forproviding power to the plasma during these changing load resistanceconditions by way of an inverter 120 (controlling for example the ACfrequency of a square wave pulse signal) and a ballast transformer 122.In this system, a leakage inductance of the ballast transformer 122serves the purposes of both a) limiting the current into a variable loadwhen driven by a fixed voltage AC source and b) providing a resonancewith cable capacitance and therefore can provide a high voltage toignite a plasma.

Circuit Analysis

FIG. 2 is a schematic circuit model of asymmetric ballast transformer122 of the present invention for coupling to a variable load Rv such asa plasma load, including but not limited to an atmospheric pressureplasma pen (discussed above) or a cutting torch (discussed below). Asshown in FIG. 1 , an AC voltage source 130 is coupled to transformer 122by coupling connections 134. The AC voltage source can provide an ACwaveform which may be sinusoidal, square wave, or other arbitrary pulsedor bi-polar waveform, and provide a waveform whose frequency can bevaried. The voltage source 130 supplies current which flows through theprimary windings 1. The current through windings 1 induce current flowthrough the secondary windings 2 of transformer 102, producing a step upor step down AC voltage which appears across the variable plasma loadRp. A coaxial connection 140 is used in this circuit to connect thetransformer 122 to the variable plasma load Rv, but other types ofelectrical interconnects with or without filtering could be used inaddition or instead of the coaxial connection 140. As shown in FIG. 1 ,a leakage inductance Ls 138 and cable capacitance 142 (from the coaxialcable) appear in this circuit.

A plasma, when fully formed, would appear in the circuit schematic ofFIG. 2 as a resistance Rp, here between 0.3-5 kOhms. However, beforeplasma ignition, Rp is 100's of thousands or millions of Ohms andimmediately after ignition is less than 2 Ohms. Note that the currentTPiOut is in waveshape nearly the same as current TPIXFMR (i.e., aplasma drive current waveform) on driving side since every transformeris a current transformer. As a close approximation, the magnitude ofTPiOut current is nearly TPIXFMR/N, the turns ratio which is known ordiscoverable. Therefore, it is not necessary to measure current with aspecial device on the secondary or plasma side where higher voltages andhigher noise may exist. The ability to measure or calculate thesecondary current without a separate and potentially expensive orphysically large device is one advantage of the present invention.

To address the issue of the maintenance of proper operational states ofan atmospheric pressure plasma, the present invention discovered that,through the monitoring of plasma drive current waveforms (e.g.,TPIXFMR), both proper and improper operational states of the atmosphericpressure plasma can be determined. Accordingly, in one embodiment of theinvention, there is provided a programmed microprocessor (such ascontrol 116 shown in FIGS. 2A and 2B) configured to detect the state ofa plasma by monitoring the plasma drive current waveform (e.g.,TPIXFMR). The microprocessor can be programmed to make decisions as towhat action(s) to take based on for example one or more of a) thewaveshape of the plasma drive current waveforms, b) the amplitude andoperating sequence of the plasma drive current waveform (for example didthe plasma form when expected in the startup phase or is it too hot orweak during the work phase), and c) resonances appearing in the drivecurrent waveforms.

There are a number of process variables (discussed below) which canaffect an atmospheric plasma (its ignition and maintenance). In oneembodiment of the invention, the effect of such process variables on theatmospheric plasma can be determined via monitoring of the plasma drivecurrent waveform(s), with for example a microprocessor (such as control116 shown in FIGS. 2A and 2B) programmed with correlation or spectralanalysis software in order to monitor not only the plasma drive currentwaveform, but also for example the plasma gas supply, the inverter drivecurrent, and the correlation coefficient.

In one embodiment of the invention, a microprocessor determines andstores for example the correlation coefficient (e.g. nominally at 0.1),a Fourier component relative phase (e.g., from 0 to 180 degrees), air orgas supply in SLM, Standard Liters/Minute, a pressure provided into aknown air supply line and plasma generator hardware, and/or drivecurrent in amperes rms and peak to peak type (e.g. 10 to 18 A_(rms) or15 to 50 A_(p-p)).

In general, ballast transformers have a leakage inductance L_(s) thatappears in a simple analysis to be a separate inductor (leakageinductor) in series with the primary and or the secondary. If theleakage inductance L_(s) is sufficiently large, the present inventorshave realized that this inductance will serve both a) to limit thecurrent into a variable load when driven by a fixed voltage AC sourceand b) to provide a resonance with the cable capacitance and thereforecan provide a high voltage to ignite a plasma.

Asymmetric Ballast Transformer

FIG. 3 is a schematic of a ballast transformer of the present invention.The ballast transformer of FIG. 3 is shown as an illustrative way forthe present invention to couple power to a plasma (i.e., a powercoupler) As shown in FIG. 3 , a magnetic flux circuit comprises atransformer core 300 forming a magnetic loop (which could include airgaps not shown) linking a primary side 302 of the transformer to asecondary side 312 of the transformer. The primary side 302 comprises afirst primary winding 304 of wire W1 on bobbin 306. Wire W1 connects toan AC power source (not shown in FIG. 3 ), but similar to voltage source130 in FIG. 2 . The secondary side 312 comprises a second winding 314 ofwire W2 on bobbin 316. Wire W2 connects to a variable load not shown inFIG. 3 , but similar to variable load Rv in FIG. 2 .

In FIG. 3 , bobbin 316 is illustrated for a high voltage secondary.Bobbin 316 has wire W1 wound around it. In one embodiment of theinvention, bobbin 316 fits inside primary bobbin 326 to provide couplingthereto. The position of primary bobbin 326 on the second pole can varyfrom design to design to provide an adjustable coupling to the secondarywinding 324 and/or to the transformer core 300. Primary bobbin 326typically has a lower coupling to the transformer core than either thesecondary winding 324 or the primary winding 304 on bobbins 316 and 306,respectively.

Accordingly, in one embodiment of the invention, the primary winding ontransformer core 300 is split by the presence of second primary winding324 in proximity to (e.g., wrapped around or coaxially surrounding) thesecondary winding 314. This second primary winding 324 (connected inseries with the winding primary winding 304) can be a non-coaxial and/ora coaxial winding relative to the secondary winding 314 so that it ispossible to control the coupling coefficient (leakage inductance) andoptimize the trade-off between maximum flux density, core heating, andwire losses without the necessity of auxiliary adjustable flux paths. Inone embodiment, the relative positions of bobbin 306, bobbin 316, and/orbobbin 326 to the transformer core (and/or to each other) can beadjusted or can otherwise be fixed at different relative positions.

In one embodiment of the invention, the primary bobbin 306 (as notedabove) is offset from primary side 302 of the transformer core. Thisoffset allows magnetic flux to leak out and be intercepted by secondprimary winding 324 wound on bobbin 326.

In one embodiment of the invention, one of the primary or secondarywindings provides tight coupling while the other provides loose couplingwhile simultaneously providing a) enough leakage inductance to limitflux density to a safe level, b) at least a turns ratio to develop theoperating or developed plasma voltage and more, and c) a reasonableleakage inductance for resonance condition for ignition and use thatsame leakage inductance for ballast when there is a developed plasma. Inone embodiment of the invention, the leakage is adjusted by constructionof the ballast transformer components so as not to change the turnsratio all the while keeping the transformer compact while avoiding extraferrite flux path elements.

Accordingly, in one embodiment of the invention, the ballast transformerhas a magnetic core, a first primary winding on a first side of themagnetic core and connected to the AC power source, a secondary windingon a second side of the magnetic core, and a second primary windingconnected in series with the first primary winding and wound coaxial tothe secondary winding on the second side of the magnetic core, and theleakage inductance is generated by second primary winding connected inseries with the first primary winding. However, the present invention isnot limited to this configuration.

Below are details of a constructed asymmetrical ballast transformer ofthe present invention.

Ballast Transformer Design Operational Input: Pulsed 300 V above groundsignal at pulse frequency from 20-500 kHz Transformer Design: PrimaryRating: 230 VAC Epoxy coating or other coating to hold primary wire andsecondary wire in place on bobbins and to prevent vibration in use.First Primary Winding: wire size #12 AWG, 1-15 turns First PrimaryWinding Inductance: 0.5-10 μH at 10 KHz, no core Second Primary Winding:wire size #12 AWG, 1-15 turns Second Primary Winding Inductance: 0.5-10μH at 10 KHz, no core Total Primary Windings: 2-30 turns Total PrimaryWinding Inductance: 500-2000 pH at 10 KHz, with core, Q = 300 SecondaryWinding: wire size #22 AWG, ~200 turns, layered windings SecondaryWinding Inductance: 100 to 1000 μH at 10 kHz, no core 50 to 5000 mH at10 kHz, with core, Q = 500 Measured Leakage Inductance: 5-100 μH at 10kHz, with core, Q = 30

Typically, for the asymmetrical ballast transformer of the presentinvention, a coupling coefficient is about 0.97, and a magnetizationinductance (inductance of the primary winding 304 and secondary winding314) is about 30 times greater than the leakage inductance. According toone embodiment of the invention, the leakage inductance is preferably ofa value that limits current in the primary side at the instant theplasma ignites. Plasma ignition represents a tremendous change inimpedance from that of an open circuit prior to ignition to thatappearing almost as a short circuit after plasma ignition.

Further, the numerical values given below are merely illustrative andnot limiting of an asymmetrical ballast transformer of the presentinvention. Typical values for operation of the ballast transformer ofthe present invention are 0-350 mTeslas, 0.97 coupling on primary, netloss <50 W between 20-500 kHz, 1 kV-50 kV peak volts pre-ignition,0.50-5 kV volt peak operating, 0 volts output post-ignition state.

FIG. 4 is a graph of frequency vs impedance sweep characteristic of theballast transformer circuit for a “no plasma” case and for a developedplasma case. Two points/frequencies marked are for plasma operation (tothe left, 90.27 kHz) and pre-ignition (to the right, 149.6 kHz). Thesefrequencies will vary with a particular coax cable type and length (FIG.2 , coaxial cable 140 and its cable capacitance 142). If the cablecapacitance changes, the operating points/frequencies change for thesame output. Note the scale depicted is magnitude dB relative to 1 voltat the output of the cable (i.e. at the pen/torch/plasma port). 80 dBvolt is 10,000 volts. 68 dB volt is 2,500 volts amplitude or peak. InFIG. 4 , the no plasma curve represents a very high load impedance (herecalculated for 100 k Ohms, but it may be 1 megaohm or higher). In FIG. 4, the fully developed plasma curve represents a load of 2000 Ohms. Thetype of pen/torch used for these calculations was assumed to be a highvoltage plasma type with a relatively high impedance while running.

In one embodiment of the invention, the frequency of operation can bemoved from 149.6 kHz toward a lower frequency (toward the peak resonancefrequency) in order to develop higher ignition voltages (than wouldexist at 149.6 kHz) and thereafter moved to even lower frequencies (onceignited) to couple more plasma power once ignited and developed.

One plasma condition that is not shown in FIG. 4 is the stateimmediately post ignition when the plasma is very small in size and hasan impedance of 1 Ohm or less. This condition is depicted in FIG. 5 , agraph comparing input current for pre-ignition and post-ignition. InFIG. 5 , the scale on the right is in dB Amperes relative to 1 Amperepeak. Specifically, FIG. 5 shows the input current as a function offrequency for a no load pre-ignition, and shows the input current as afunction of frequency for a 1 Ohm post-ignition state (not a fullydeveloped plasma). At startup, the input current with no load condition(simulation is 100 k Ohms) is at about 32 dB or 39.8 Amperes peak. Whenthe plasma ignites, the input current is relatively small and has arelatively low impedance as compared to the fully developed plasma stateand simulated here with a resistance 1 Ohm. Note that the input currentat plasma ignition actually drops to about 21 dB or 11.2 Amperes peak.Thereafter, as shown in FIG. 6 , the plasma develops (expands) and theinput current increases as the frequency of operation is lowered to90.27 kHz or lower.

More specifically, as the plasma develops, the impedance increasesmoving the current from the post-ignition current curve to theplasma-run current curve, and the frequency is adjusted to 90.27 kHz inthis example to develop full power. Thus the ballast transformer is usedto permit the system to generate ignition voltages (FIG. 4 ), withstandthe sudden load transition from very high to near shorted conditions(FIG. 5 ) and then smoothly move to full power plasma (FIG. 6 ).

Waveform Informational Content

Normally, it is not easy or routine to obtain the output voltagewaveform or amplitude on a stepped up/load side of a ballast transformerusing conventional means. In general, it is not desirable to measureoutput voltage directly on the stepped up/load side because the systemin certain embodiments can operates up to 2-50 kV. Such high voltagemeasurement devices are large, expensive and subject to humidityeffects, corona degradation, and surface contamination, owing to theirhigh impedance operation. For a ballast transformer, input voltageremains the same whether the output load is very high impedance, normal,or even a short. Yet, the present invention has found that, unlike theprimary drive voltage, the primary drive current waveshape changessubstantially when the load is changed.

FIG. 7 is a schematic depiction showing an analysis of the circuit shownin FIG. 2 driven with a square wave voltage pulse at TPVin. FIG. 7 showsthe voltage waveform on the secondary side of the transformer at TPVoutas output volts and at TPIXFMR (i.e., the plasma drive waveform) astransformer input current. In Region 1, there is no plasma, and thus nocircuit load. Under this condition, circulating current builds upvoltage and current in the secondary side of the ballast transformeruntil there is an arc in the electrode gap in the pen/torch of theatmospheric plasma source. In Region 1, the current waveform at TPIXFMRis roughly sinusoidal. This is the “no plasma” state. Control 116 isprogrammed to recognize this roughly sinusoidal waveform as the “noplasma state” operational condition.

When the arc happens at the arc discharge point, there is a reduction ofthe voltage on the secondary side caused by the coaxial cable 140ringing down (over a short time) to zero volts because the load (thearc) is a short, i.e., a low resistance, to ground. Under this conditionin Region 2 as shown on FIG. 7 , the current trace then transitions to asawtooth with straight line segments. A square wave voltage drivenaturally creates straight current line segments with a short as loadbecause:

${V = {{- L_{s}}\frac{di}{dt}}}{\frac{di}{dt} = \frac{- V}{L_{s}}}$

The slope or rate of change for I, current, is constant because V isconstant during any half cycle (square voltage wave drive) and L_(s) isa constant. Region 2 is the “plasma origination” state. Control 116 isprogrammed to recognize this sawtooth pattern with straight linesegments as the “plasma origination” state.

FIG. 8 is a reproduction of an actual scope trace showing the sawtoothplasma drive current waveform and the voltage drive in Region 2.Eventually, the plasma grows until there is a resistive plasma loadresulting in an instantaneous current that rises in a classic R/L orexponential curve to an asymptotic value:

$i = {i_{o}\left( {1 - e^{- {({R_{pen}\frac{t}{L_{s}}})}}} \right)}$

FIG. 9 is a schematic depicting a simulated current waveshape for adeveloped plasma occurring in Region 3 shown in FIG. 7 . Notice in FIG.9 that the drive phase reverses before a final settled current value isreached. Region 3 is the “plasma maintenance” state operating with asignificant resistive plasma load. Control 116 is programmed torecognize this exponential curve or asymptotic value approaching patternas the “plasma maintenance” state.

Hence, in one embodiment of the invention, programmed control 116 canidentify the state of plasma formation by analyzing the primary currentwave shape at TPIXFMR in the primary without having special probes onthe high voltage secondary. Also, it is possible to use the primarydrive voltage and primary current together to find input power asfollows:

${P = {i^{2}R_{pen}}}{R_{pen} = \frac{P}{i^{2}}}$

Control 116 in one embodiment can calculate plasma resistance so thatthe measured plasma resistance confirms a plasma operational state.

In one embodiment, control 116 can determine a particular plasma drivewaveform shape by autocorrelation with a set of suitably scaled andshifted sample waveforms such that the autocorrelation with highestcorrelation coefficient is then a determination of the closest prototypeshape, and thus determines which operational state exists at that time.

In one embodiment, control 116 can determine a particular plasma drivewaveform shape by a Fourier Series Analysis, in which a correlation withthe sine and cosine of the 1st and 3rd harmonics, deriving a relativeangle between them. This is possible with control 116 beingpreprogrammed with the bridge drive voltage pulse shape and analog todigital conversion (ADC) sample frequencies so that control 116 knowsthe number of ADC samples per bridge cycle. Typically, only two bridgecycles of analysis are sufficient. It is not necessary to find the drivecycle phase as long as two complete cycles' worth of ADC samples isused. Note that using more complete inverter cycles for the Fourier orspectral analysis is equivalent to running through a longerautocorrelation analysis and serves to reject noise. The waveshapeinformation is contained in the current's spectral angle.

Note that other mathematical analysis/transformation techniques besidesa Fourier Series Analysis can be used by control 116 for analysis ofwaveform. Further, the waveform analysis need not necessarily be in thefrequency domain but could be in the time domain More generally, itcould be considered harmonic analysis. Other such techniques for use bythe invention include wavelet and chirplet transforms

FIG. 10 is a schematic depicting computed current transfer functionamplitudes for various output loads. From the dashed frequency markerline in FIG. 10 and high in frequency for a typical output network, thecurrent transfer spectrum is nearly the same for loads of 0.3-5 kOhms tovery low values like 1 Ohm, a short. Drive spectrum remains the same,exhibiting odd harmonics for a square wave. Therefore, the currentspectrum is controlled primarily by the load impedance.

FIG. 11 is a current amplitude spectrum from a square wave drive into aballast transformer for nominal plasma impedance. FIG. 12 is a currentamplitude spectrum from a square wave drive into a ballast transformerfor a 1 Ohm short. In both cases, the 1st and 3rd harmonics have thesame ratio, about 25 dB. Therefore, the relative angle is required forcurrent waveshape ID. The vertical dotted frequency marker line is theinverter drive frequency, with the associated odd harmonics following tothe right.

The current frequency transfer function of a developed plasma load(illustrated above in FIG. 7 ) shows that harmonics above the 3rd orderare typically suppressed in Region 3 (i.e., in the operating or plasmamaintenance state). Therefore, in one embodiment of the invention, aFourier series is produced for 1st and 3rd harmonics only. Operation inthe plasma state can be made or confirmed by observing the 1st amplitudeand phase angle between 1st and 3^(rd) and/or by comparing these metricsto those in Region 2 of the plasma origination state. The harmonics inRegion 2 or in the plasma origination state nominally should have arelative phase of near zero, and typically the 3rd amplitude should notbe below 5% of the 1^(st) harmonic amplitude during normal operation.Also, typically, the 1st harmonic amplitude of the current shouldnominally be between 8 to 15 A_(rms), although this value may be scaledup or down depending on the size of the plasma.

A relative angle above 45 degrees means that the plasma has transitionedfrom the plasma origination state to the plasma maintenance state, i.e.,Region 3, the operating state. In one embodiment, a maximum of 130degrees is used as an upper limit for the relative angle indicating thatthere is sufficient but not too much curve in the waveform. Therefore,relative angle determination can be used to determine that the plasma isdeveloped and in a successful startup or continuing operation.

The utility of this analysis is that a low phase shift indicates aRegion 2 startup triangle waveform (i.e., the plasma origination mode)which should not appear at any time during operation. If a low phaseshift condition occurs, that would mean the plasma is undeveloped andnear zero ohms, e.g., a small ignition spark. If left in this condition,the electrodes would soon be damaged. Also, there is no useful plasmaunder this condition. The software in control 116 is written to know totake corrective action which is for example at least to stop drivevoltage, terminating the plasma and saving the electrodes (which arecoupling power into the atmospheric pressure plasma). A loss of airpressure and flow into the system could cause this condition. A shortedplasma torch/pen cable or connector could also cause this condition. Ablocked orifice could also cause this condition. Regardless, with thepresent invention, separate detectors (for any of these events such asan air pressure indicator or cable test circuit) are not needed (butcould be used to supplement the present invention).

In short, as the air flow changes to a lower value or the plasmaelectrodes become too hot or the orifice becomes restricted but notblocked, the plasma drive waveform will begin to transition to astraight line and the phase angle difference will become lower andlower. In one embodiment of the present invention, control 116 can issuea system warning or a warning specifically to the operator of theatmospheric plasma system of the degrading plasma state. This warningcan be issued when the plasma is exhibiting the same or nearly the sameperformance, and thus undetectable by the operator. This warning can beissued for example as a warning to the operator of a falling air flowcondition which may to the operator appear satisfactory but when inreality it is not. Further, the control 116 can monitor the system as itages and set a time for maintenance based on the age progression.

Plasma Waveform Discrimination

In this embodiment, an inverter output (shown schematically in FIG. 13 )is used to drive a ballast transformer. Typically, four (4) highcurrent, low loss, switching transistors are arranged in a full bridgecircuit topology, with the plasma drive waveform being generated by aSystem on a Chip (SOC) microprocessor producing complementary transistorgate drive output waveforms. As shown in FIG. 13 , a square waveinverter outputs voltage signals to the primary side of the ballasttransformer. In one embodiment, a current sampling circuit is connectedin series with the ballast transformer. In one embodiment, the currentsampling circuit is a current sense transformer (CST) measuring currentin the primary side of the ballast transformer. Analog outputs of theCST representative of the plasma current drive waveform are directed tothe analog to digital converter (ADC) which in this embodiment is partof the SOC microprocessor shown on FIG. 13 . The SOC microprocessorshown on FIG. 13 could be part of control 116 in FIGS. 1A and 1B.

Specific details of a suitable current sampling circuit for the presentinvention are shown in FIG. 14 . In FIG. 14 , the current samplingcircuit is connected at CSTPort where an appropriate current sensingtransformer CST is provided. Current through the primary of the CSTcontinues out of the current sampling circuit into the primary of theballast transformer. The secondary side of the CST is connected inseries with a load to set the current in the CST secondary to a suitablevoltage conversion range by the current flowing through resistive loadsR90 R34. C27 and D13 are simple DC Restorer circuits which change the ACwaveform to a 0 to ‘Y’ range of the same amplitude. This change in thewaveform is needed because the ADC in the SOC cannot handle negativevoltages, but the information content is the same regardless of thischange. Output from the 0 to 1.5 Vp or volt peak output is taken andconnected to the input of the SOC ADC to produce a digital waveformtrace.

Inside the SOC, in one embodiment, the ADC is arranged to run at least 8times the rate of the inverter cycle rate. The preferred method is 20times or more so that the waveform curve can be seen clearly in thefewest drive cycles. The relationship between the bridge drive and ADCsample rate which are both running from the same internal clock and thushave a fixed timing relationship for any particular ADC and directmemory access (DMA) transfer, is used to select any sequential 2-timesor indeed N-times integral ADC sample cycles and perform a Fourierseries analysis on one the 1st and 3rd harmonics sine and cosinecorrelation analysis without bothering to normalize. The fundamentalphase angle as captured compared to the 1^(st) sample is:

a tan (1^(st) imaginary/1^(st) real)

The 3^(rd) harmonic angle relative to the first sample is:

a tan (3^(rd) imaginary/3^(rd) real)

The real series is that correlated with cosine function and theimaginary is that correlated with the sine function. An adjustment isthen made by adding or subtracting 180 degrees to bring the 1^(st) and3^(rd) angles into the 1^(st) & 2^(nd) quadrant, and then they aresubtracted. This is equivalent to finding the first zero crossing ofeach and subtracting sample indices then converting that to 1^(st)degrees by normalizing with degrees per sample. Then 180 degrees isadded or subtracted to bring into the 1^(st) and 2^(nd) quadrants. Theresulting angle is the 1^(st) & 3^(rd) difference angles at the 1^(st)frequency. If this difference is less than 45 degrees when the plasmashould be fully developed and operating in Region 3 of FIG. 5 ,controller 212 is programmed to throw a fault and set an alarm to theoperator(s) to look for a problem. This recognition of a fault and thesetting of the alarm can be all possible from one capture of the primarycurrent waveform.

As noted above, a ballast transformer is but one way for the presentinvention to couple power to a plasma/Other power couplers can be usedbesides a transformer with this inventive method of waveform analysisworking for a “transformer-less” plasma power supplies. Transformer-lesspower supplies are power supplies that can switch directly from a veryhigh voltage source. For example, an inverter that operates at 25,000volts and is able to switch the 25,000 volt DC into any arbitrary highvoltage, high frequency waveform can provide power to a plasma. The useof a current sense transformer (CST) on the high voltage line of thistype of inverter would permit similar analysis, with a high voltage CSTbeing made relatively small

A number of advantages are provided by the inventive system where theplasma state is ascertained from analysis of the plasma drive currentwaveforms. Some of these advantages include:

1. Current and/or especially voltage detection on the high voltage andpower/load side of a transformer is not needed.

2. Only a few current sampling acquisitions are needed in order todetermine a plasma operational state.

3. Waveshape analysis shows that the amplitude of the 1st and 3rdharmonics in the plasma drive current waveform are sufficient fordetermining if the gas pressure or gas flow rate is adequate for plasmamaintenance without the need for separate gas pressure and flowratesensors.

4. Repeated waveform analysis over time can identify developing faultsin the plasma condition without need for separately installed faultdetectors since repeated waveform analysis provides knowledge of theplasma condition as a function of time.

5. The power dissipated can be measured at the same time that the plasmadrive current waveform is measured using a bridge DC measurement deviceand software integrating the average drive voltage and bridge outputcurrent product.

6. The relative (or exact) plasma impedance, and thus the resistance andapproximate temperature and thereby the plasma density or charge carriercondition in the plasma can be deduced from the waveshape and simulationof the output network.

Computer Control

It will be understood that the control 116 schematically illustrated inFIGS. 1A and 1B may also be representative of one or more types of userdevices, such as user input devices (e.g., keypad, touch screen, mouse,and the like), user output devices (e.g., display screen, printer,visual indicators or alerts, audible indicators or alerts, and thelike), a graphical user interface (GUI) controlled by software fordisplay by an output device, and one or more devices for loading mediareadable by control 116 (e.g., logic instructions embodied in software,data, and the like). Control 116 may include an operating system (e.g.,Microsoft Windows® software) for controlling and managing variousfunctions.

FIG. 15 is a flowchart detailing a method of the present invention fordetecting an operational state of an atmospheric pressure plasma.

In step 1501, at least one current pulse flowing through a primarywinding of a transformer coupling power is measured (sampled or sensed).

In step 1503, from a waveform of the current pulse, the operationalstate of the atmospheric pressure plasma is determined.

In optional step 1505, the determination can occur by associating ashape of the waveform with a particular operational state of theatmospheric pressure plasma. As noted above, a sinusoidal waveform isindicative of a “no plasma state,” a sawtooth waveform with straightline segments is indicative of the “plasma origination state” in whichan arc ignited in the plasma chamber is expanding into a plasma by gasflow thereinto, and an asymptotic waveform is indicative of the “plasmamaintenance state.”

In optional step 1507, the determination can occur by analyzingharmonics of the waveform and comparing the magnitudes of the 1^(t) and3^(rd) harmonics, and realizing that, with the plasma maintenance statehaving the highest (plasma) load resistance, higher harmonics would besuppressed.

In optional step 1509, the determination can occur by determining fromthe waveform a real power in each pulse being dissipated, and realizingthat, in the plasma maintenance state, the plasma load resistance is thehighest.

Moreover, while not shown, in step 1503, a relative angle between a) thevoltage pulse applied to the primary winding and b) the waveform of thecurrent pulse can be calculated, and based on the relative angle betweena) the voltage pulse applied to the primary winding and b) the waveformof the current pulse, the operational state of the atmospheric pressureplasma can be ascertained. For example, as noted above, when the plasmaorigination state matures into the plasma maintenance state, a relativeangle between current and voltage is observed to be above 45 degrees.

It will be understood that one or more of the processes, sub-processes,and process steps described herein may be performed by hardware,firmware, software, or a combination of two or more of the foregoing, onone or more electronic or digitally-controlled devices for exampleadjusting the variable capacitors and/or the relative bobbin positionsand/or the power level of the AC source. The software may reside in asoftware memory (not shown) in a suitable electronic processingcomponent or system such as, for example, the control 116 schematicallydepicted in FIGS. 1A and 1B. The software memory may include an orderedlisting of executable instructions for implementing logical functions(that is, “logic” that may be implemented in digital form such asdigital circuitry or source code, or in analog form such as an analogsource such as an analog electrical, sound, or video signal). Theinstructions may be executed within a processing module, which includes,for example, one or more microprocessors, general purpose processors,combinations of processors, digital signal processors (DSPs), orapplication specific integrated circuits (ASICs). Further, the schematicdiagrams describe a logical division of functions having physical(hardware and/or software) implementations that are not limited byarchitecture or the physical layout of the functions. The examples ofsystems described herein may be implemented in a variety ofconfigurations and operate as hardware/software components in a singlehardware/software unit, or in separate hardware/software units.

The executable instructions may be implemented as a computer programproduct having instructions stored therein which, when executed by aprocessing module of an electronic system (e.g., the control 116schematically depicted in FIGS. 1A and 1B), direct the electronic systemto carry out the instructions. The computer program product may beselectively embodied in any non-transitory computer-readable storagemedium for use by or in connection with an instruction execution system,apparatus, or device, such as a electronic computer-based system,processor-containing system, or other system that may selectively fetchthe instructions from the instruction execution system, apparatus, ordevice and execute the instructions. In the context of this disclosure,a computer-readable storage medium is any non-transitory means that maystore the program for use by or in connection with the instructionexecution system, apparatus, or device. The non-transitorycomputer-readable storage medium may selectively be, for example, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, or device. A non-exhaustive list ofmore specific examples of non-transitory computer readable mediainclude: an electrical connection having one or more wires (electronic);a portable computer diskette (magnetic); a random access memory(electronic); a read-only memory (electronic); an erasable programmableread only memory such as, for example, flash memory (electronic); acompact disc memory such as, for example, CD-ROM, CD-R, CD-RW (optical);and digital versatile disc memory, i.e., DVD (optical). Note that thenon-transitory computer-readable storage medium may even be paper oranother suitable medium upon which the program is printed, as theprogram can be electronically captured via, for instance, opticalscanning of the paper or other medium, then compiled, interpreted, orotherwise processed in a suitable manner if necessary, and then storedin a computer memory or machine memory.

It will also be understood that the term “in signal communication” asused herein means that two or more systems, devices, components,modules, or sub-modules are capable of communicating with each other viasignals that travel over some type of signal path. The signals may becommunication, power, data, or energy signals, which may communicateinformation, power, or energy from a first system, device, component,module, or sub-module to a second system, device, component, module, orsub-module along a signal path between the first and second system,device, component, module, or sub-module. The signal paths may includephysical, electrical, magnetic, electromagnetic, electrochemical,optical, wired, or wireless connections. The signal paths may alsoinclude additional systems, devices, components, modules, or sub-modulesbetween the first and second system, device, component, module, orsub-module.

More generally, terms such as “communicate” and “in . . . communicationwith” (for example, a first component “communicates with” or “is incommunication with” a second component) are used herein to indicate astructural, functional, mechanical, electrical, signal, optical,magnetic, electromagnetic, ionic or fluidic relationship between two ormore components or elements. As such, the fact that one component issaid to communicate with a second component is not intended to excludethe possibility that additional components may be present between,and/or operatively associated or engaged with, the first and secondcomponents.

EXEMPLARY STATEMENTS OF THE INVENTION

The following numbered statements of the invention set forth a number ofinventive aspects of the present invention:

Statement 1. A system for determining an operational state of anatmospheric pressure plasma, the system comprising:

a power coupler for coupling power into the atmospheric pressure plasma;

a current sampling circuit configured to sample at least one currentpulse flowing through a primary winding of the transformer; and

a programmed microprocessor configured to determine, from a waveform ofthe current pulse, the operational state of the atmospheric pressureplasma,

wherein the operational state comprises one of

a no plasma state,

a plasma origination state indicative of an ignited arc expanding into aplasma by gas flow thereinto, and

a plasma maintenance state indicative of the plasma being expanded.

Alternatively, there is provided a system for determining operationalstates of an atmospheric pressure plasma, the system comprising

a power coupler for coupling power into the atmospheric pressure plasma,

a current sampling circuit configured to sample at least one currentpulse flowing to a plasma-generating region, and

a programmed microprocessor configured to determine, from a waveform ofthe current pulse, the operational state of the atmospheric pressureplasma. The operational state is one of: a no plasma state, a plasmaorigination state indicative of an ignited arc expanding into a largervolume of plasma by gas flow thereinto, and a plasma maintenance stateindicative of the plasma being expanded.

Statement 2. The system of statement 1, wherein the current samplingcircuit comprises a current sense transformer (CST) connected to theprimary winding of the transformer. More generally, the CST is in placebetween the power coupler and the plasma generating region.

Statement 3. The system of statements 1 or 2, wherein the at least onecurrent pulse flowing through a primary winding is driven by a voltagepulse applied to the primary winding of the transformer.

Statement 4. The system of any of the statements above, including thealternative configurations, wherein the programmed microprocessorcomprises an analog to digital converter (ADC) in electricalcommunication with the current sampling circuit in order to capture adigital trace of the waveform of the current pulse for analysis.

Statement 5. The system of statement 4, wherein the programmedmicroprocessor is configured to identify from the digital trace that:

a sinusoidal waveform is indicative of the no plasma state;

a sawtooth waveform is indicative of the plasma origination state, wheresegments of the sawtooth waveform are preferably straight line segments;and

an asymptotic waveform having a section exponentially approaching anasymptotic value. (One asymptotic waveform is illustrated in the shapesdepicted in FIG. 9 .)

Statement 6. The system of statement 4, wherein the programmedmicroprocessor is configured to identify harmonics of the waveform.

Statement 7. The system of statement 6, wherein the programmedmicroprocessor is configured to ascertain the operational state of theatmospheric pressure plasma based on relative strengths of theharmonics.

Statement 8. The system of statement 4, wherein the programmedmicroprocessor is configured to

calculate a relative phase angle between a) the voltage pulse applied tothe primary winding and b) the waveform of the current pulse, and

based on the relative phase angle, ascertain the operational state ofthe atmospheric pressure plasma.

Statement 9. The system of claim 8, wherein the programmedmicroprocessor is configured to calculate an average current in thecurrent pulse, and an average voltage of the voltage pulse, and therebya real power being dissipated, and

based on the real power, ascertain the operational state of theatmospheric pressure plasma.

Statement 10. The system of any of the statements above, furthercomprising an inverter (e.g., a square wave inverter) configured toproduce voltage pulses at a predetermined frequency for application tothe primary winding of the transformer.

Statement 11. The system of statement 1, wherein the transformercomprises a ballast transformer having

-   -   a magnetic core,    -   a primary winding on a primary side of the magnetic core,    -   a secondary winding on a secondary side of the magnetic core,        and

wherein

the primary winding is connectable to a power source, and

the secondary winding is connectable to a plasma load of the atmosphericpressure plasma.

Statement 12. The system of statement 11, wherein the ballasttransformer comprises a resonant transformer having a resonanceassociated with a capacitance and an inductance appearing across openends of the secondary winding.

Statement 13. The system of statement 11, wherein the secondary windinghas more turns than the primary winding such that the transformercomprises a step-up transformer for supplying current to the atmosphericpressure plasma.

Statement 14. The system of statement 11, wherein the primary windingcomprises a first primary winding and a second primary winding.

Statement 15. The system of claim 14, wherein the first primary windingand the second primary winding provide an inductive impedance thatopposes current surges when a load is introduced.

Statement 16. The system of statement 14, wherein the second primarywinding is displaceable from the secondary winding to alter a couplingcoefficient of the transformer.

Statement 17. The system of statement 14, wherein the second primarywinding coaxially surrounds the secondary winding.

Statement 18. The system of statement 14, wherein the second primarywinding is offset axially from and surrounds the secondary winding.

Statement 19. The system of any of the statements above, furthercomprising:

an inverter configured to produce voltage pulses at a predeterminedfrequency for application to the primary winding of the transformer (theinverter can produce square wave pulses, non-square pulses, sinusoidalpulses, or any arbitrary pules generated for example from a modulatedbipolar drive);

an analog to digital converter (ADC) in electrical communication withthe current sampling circuit in order to capture a digital trace of thewaveform of the current pulse for analysis.

Statement 20. The system of statement 19, wherein the microprocessor,the square wave inverter, and the analog to digital converter (ADC)comprise a system on chip (SOC) component comprising a controller forthe system.

Statement 21. A method for determining an operational state of anatmospheric pressure plasma using any of the systems described in thestatements above.

Statement 22. The method of statement 21, wherein the method comprises:

sampling at least one current pulse flowing through a primary winding ofa transformer coupling power into the atmospheric pressure plasma; and

determining, from a waveform of the current pulse, the operational stateof the atmospheric pressure plasma.

Alternatively, there is provided a method which samples at least onecurrent pulse flowing into the atmospheric pressure plasma; anddetermines, from a waveform of the current pulse, the operational stateof the atmospheric pressure plasma.

Statement 23. The method of statement 22 and its alternative, whereinthe determination occurs by associating a shape of the waveform with aparticular operational state of the atmospheric pressure plasma.

Statement 24. The method of statement 22, wherein the determinationoccurs by analyzing harmonics of the waveform.

Statement 25. The method of statement 22, wherein the determinationoccurs by determining from the waveform a real power in each pulse beingdissipated, and realizing that, in the plasma maintenance state, theplasma load resistance is the highest.

Statement 26. The method of statement 22, wherein the determinationoccurs by calculating a relative phase angle between a) the voltagepulse applied to the primary winding and b) the waveform of the currentpulse, and based on the relative phase angle, ascertaining theoperational state of the atmospheric pressure plasma.

Statement 27. A ballast transformer as described above in any of thestatements 11-18 and whose operation is controlled in part by thesystems described in any of the statements above.

Numerous modifications and variations of the invention are possible inlight of the above teachings. It is therefore to be understood thatwithin the scope of the appended claims, the invention may be practicedotherwise than as specifically described herein.

The invention claimed is:
 1. A system for determining an operationalstate of an atmospheric pressure plasma, the system comprising: atransformer for coupling power into the atmospheric pressure plasma; acurrent sampling circuit configured to sample at least one current pulseflowing through a primary winding of the transformer; and a programmedmicroprocessor configured to determine, from a waveform of the currentpulse, the operational state of the atmospheric pressure plasma, whereinthe operational state comprises one of a no plasma state, a plasmaorigination state indicative of an ignited arc expanding into a largerplasma volume by gas flow thereinto, and a plasma maintenance stateindicative of the plasma being expanded into the desired volume andsteady-state condition, wherein the programmed microprocessor isconfigured to calculate a relative phase angle between a) a voltagepulse applied to the primary winding and b) the current pulse flowingthrough the primary winding, and based on the relative phase angle,ascertain the operational state of the atmospheric pressure plasma. 2.The system of claim 1, wherein the current sampling circuit comprises acurrent sense transformer (CST) connected across the primary winding ofthe transformer.
 3. The system of claim 1, wherein the at least onecurrent pulse flowing through a primary winding is driven by a voltagepulse applied to the primary winding of the transformer.
 4. The systemof claim 3, wherein the programmed microprocessor comprises an analog todigital converter (ADC) in electrical communication with the currentsampling circuit in order to capture a digital trace of the waveform. 5.The system of claim 4, wherein the programmed microprocessor isconfigured to identify from the digital trace: a sinusoidal waveformthat is indicative of the no plasma state; a sawtooth waveformindicative of the plasma origination state, where segments of thesawtooth waveform are straight line segments; and and an asymptoticwaveform having a section exponentially approaching an asymptotic value.6. The system of claim 4, wherein the programmed microprocessor isconfigured to identify harmonics of the waveform.
 7. The system of claim6, wherein the programmed microprocessor is configured to ascertain theoperational state of the atmospheric pressure plasma based on relativestrengths of the harmonics.
 8. The system of claim 1, wherein theprogrammed microprocessor is configured to calculate an average currentin the current pulse, and an average voltage of the voltage pulse, andthereby a real power being dissipated, and based on the real power,ascertain the operational state of the atmospheric pressure plasma.
 9. Asystem for determining an operational state of an atmospheric pressureplasma, the system comprising: a transformer for coupling power into theatmospheric pressure plasma; a current sampling circuit configured tosample at least one current pulse flowing through a primary winding ofthe transformer; and a programmed microprocessor configured todetermine, from a waveform of the current pulse, the operational stateof the atmospheric pressure plasma, wherein the operational statecomprises one of a no plasma state, a plasma origination stateindicative of an ignited arc expanding into a larger plasma volume bygas flow thereinto, and a plasma maintenance state indicative of theplasma being expanded into the desired volume and steady-statecondition, further comprising a square wave inverter configured toproduce voltage pulses at a predetermined frequency for application tothe primary winding of the transformer, wherein the transformercomprises a ballast transformer having a magnetic core, a primarywinding on a primary side of the magnetic core, a secondary winding on asecondary side of the magnetic core, and wherein the primary winding isconnectable to a power source, and the secondary winding is connectableto a plasma load of the atmospheric pressure plasma.
 10. The system ofclaim 9, wherein the ballast transformer comprises a resonanttransformer having a resonance associated with a capacitance and aninductance appearing across open ends of the secondary winding.
 11. Thesystem of claim 9, wherein the secondary winding has more turns than theprimary winding such that the transformer comprises a step-uptransformer for supplying current to the atmospheric pressure plasma.12. The system of claim 9, wherein the primary winding comprises a firstprimary winding and a second primary winding.
 13. The system of claim12, wherein a leakage inductance of the transformer opposes currentsurges when a plasma is initiated.
 14. The system of claim 12, whereinthe second primary winding is displaceable from the secondary winding toalter a coupling coefficient of the transformer.
 15. The system of claim12, wherein the second primary winding wraps around the secondarywinding.
 16. The system of claim 12, wherein the second primary windingis offset axially from the secondary winding.
 17. The system of claim 1,further comprising: an inverter configured to produce voltage pulses ata predetermined frequency for application to the primary winding of thetransformer; an analog to digital converter (ADC) in electricalcommunication with the current sampling circuit in order to capture adigital trace of the waveform of the current pulse for analysis.
 18. Thesystem of claim 17, wherein the microprocessor, the square waveinverter, and the analog to digital converter (ADC) comprise a system onchip (SOC) component comprising a controller for the system.